#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#define NLOOP 5000

int counter; 

/* incremented by threads */
pthread_mutex_t counter_mutex = PTHREAD_MUTEX_INITIALIZER;
void *doit(void *);

int main(int argc, char **argv)
{ 
	pthread_t tidA, tidB; 
	pthread_create(&tidA, NULL, doit, NULL); 
	pthread_create(&tidB, NULL, doit, NULL); 

	/* wait for both threads to terminate */ 
	pthread_join(tidA, NULL); 
	pthread_join(tidB, NULL); 
	return 0;
}

void *doit(void *vptr)
{ 
	int i, val; 
	/* * Each thread fetches, prints, and increments the counter NLOOP times. 
	* The value of the counter should increase monotonically. */ 

	for (i = 0; i < NLOOP; i++) 
	{ 
		pthread_mutex_lock(&counter_mutex); 
		val = counter; 
		printf("%x: %d\n", (unsigned int)pthread_self(), val + 1); 
		counter = val + 1; 
		pthread_mutex_unlock(&counter_mutex); 
	} 
	return NULL;
}